1. Technical Field
This invention relates to liquid diagnostic devices and more particularly to shields for such devices to confine the excess liquid to the diagnostic devices.
2. Background
U.S. Pat. No. 4,756,884 discloses a disposable diagnostic device in the form of a cartridge which, with the use of a monitor, can be used to substantially instantly determine the prothrombin (PT) time of one's blood. Such instantaneous determination of this and other tests is of great value both to patients and to physicians in that it permits prompt diagnosis of a disease state, prescription of appropriate medication and monitoring of the proper dosage of medication, such as the oral anticoagulant coumadin commonly called Warfarin. The assignee has also developed a diagnostic device for measuring Activated Partial Thromboplastin Time (APTT). This is the subject of co-pending U.S. Application Ser. No. 341,045, filed on Apr. 20, 1989. While the present invention has broad application beyond these specific examples, these will be used throughout this application as typical applications.
Each of these devices mentioned above is roughly the size of a conventional plastic identification or "credit" card and is a single use disposable item. Both are used with suitable monitors about the size of a small to medium-sized book and having a receiving slot therein into which the cartridge is partially inserted in preparation for the measurement. Each cartridge has a liquid receiving well which remains outside the monitor and into which the liquid to be analyzed is deposited, either directly from a pricked finger or using a capillary tube, syringe, or the like.
Two related problems and disadvantages have been recognized, and the present invention has been developed to solve both of them. One problem is the occasional, inadvertent, seepage of excess liquid from the surface of the cartridge into the interior of the monitor such that a failsafe self-diagnostic system within the monitor will prevent it from reporting test results until the monitor is cleaned. Specifically, internal sensors present in the monitors for the cartridges described above, such as light sensing transducers and other instruments, can be affected by the unintentional presence of liquid, such as blood. If, when the self-diagnostic check is being run, the readings from the sensors are outside of the expected ranges, the monitor will withhold the reporting of any test results until the readings return to the normal range.
A related problem, apart from having liquid interfere with the operation of the monitor, is the contamination of the monitor which results from contact of the liquid with either the interior or exterior of the monitor. Not only is such contact unsightly and unsanitary, but the hazards of contact with infected bodily liquids of the diagnosee, and the desirability of preventing such contact, are so apparent as to require no further elaboration. Whether the contact of the excess liquid renders the monitor completely inoperative or simply contaminates the monitor, it requires removal of the monitor from service so that it can be cleaned and repaired if necessary.
The problem of confining excess liquid to the surface of cartridges such as those disclosed in the referenced patents is complicated by a series of factors. One such factor is the desirability that the device be ready to use immediately upon its removal from its packaging. Another factor is the need for space efficient nesting of the packaged cartridges to reduce storage space requirements. Yet another consideration is that the liquid shield not change or otherwise adversely affect the design or manufacture of the cartridges, which involves some ultrasonic assembly steps requiring flat cartridge surfaces. Still another consideration is the requirement that neither the liquid shield, nor any material used to attach it, impair or interfere with the accuracy of results obtained when using the cartridge with an appropriate monitor. Further, it is desirable that new shielded cartridges be usable with monitors already in the field.